Our laboratory is currently studying growth control in the crown gall teratoma of plants. These tumors will, under appropriate conditions, produce well-formed shoots composed of tumor cells. Tumors are once again initiated if the tissue is grown in culture. Teratoma shoots will flower and set seed; the plants of the next generation show no signs of neoplastic potential and, hence, may be said to have recovered from the disease. We are studying the neoplastic potential of single, differentiated cells in teratoma shoots. We have found that epidermal hairs of teratomas will initiate tumors in culture. Other cell types are now being tested. The recovery phenomenon is also being studied by the examination of sporogenous cells undergoing meiosis and germ cell differentiation. In both these projects the capacity of cells to synthesize tumor specific metabolites (opines) is being used as a marker for the neoplastic state. The control of opine synthesis in tumor tissue is also being studied.